temp_code/swift/demo001/main.swift

import Cocoa

class AppDelegate: NSObject, NSApplicationDelegate {
    var window: NSWindow?

    func applicationDidFinishLaunching(_ aNotification: Notification) {
        window = NSWindow(
            contentRect: NSRect(x: 0, y: 0, width: 400, height: 200),
            styleMask: [.titled, .closable, .resizable],
            backing: .buffered, defer: false)
        window?.center()
        window?.title = "Hello World App"
        window?.makeKeyAndOrderFront(nil)
        
        let label = NSTextField(labelWithString: "Hello World")
        label.font = NSFont.systemFont(ofSize: 24)
        label.sizeToFit()
        label.frame.origin = CGPoint(
            x: (window?.contentView!.frame.size.width - label.frame.size.width) / 2,
            y: (window?.contentView!.frame.size.height - label.frame.size.height) / 2)
        
        window?.contentView?.addSubview(label)
    }

    func applicationWillTerminate(_ aNotification: Notification) {
    }
}

NSApplicationMain()